The invention relates to a motion-picture camera provided with a light-sensitive negative-feedback diaphragm control system, of the type including a stepper motor which adjusts the diaphragm and is driven by a control circuit which generates stepper-motor drive pulses in dependence upon the imbalance of the diaphragm control system. In motion-picture cameras of this type, fadeover effects are produced by deliberately imbalancing the diaphragm control system, to produce an aperture decrease for fadeout, and after the intermediate film rewind, a corresponding aperture increase for the subsequent fade-in. It is desired that the amount by which the aperture is changed for the fade-out and the fade-in be always the same, i.e., irrespective of the number of film frames which the photographer selects for involvement in the fadeover.
It is also desired that, during the fade-out, the speed of operation of the stepper motor progressively increase and then, during the subsequent fade-in, progressively decrease in a corresponding manner.
Most preferably, it is desired that the frequency of the oscillator producing the stepper-motor drive pulses be varied, by means of its time-constant circuit, in such a way that, at the start of the fade-out, the frequency drops from its normal-filming value down to a lower limit value, then during the fade-out progressively increases to an upper limit value higher than that for normal filming, then during the subsequent fade-in progressively decreases from the upper limit value back down to the lower limit value, and then at the end of the fade-out returns to its normal-filming value.